Radio signaling system



Nov. 6, 1945. s. w. sEELEY ET AL RADIO SIGNALING SYSTEM Filed Sept. 5, 1942 INVENTOR.

BYJoH/v AZNK/N.

ATTORNEY QNSQ wmv@ SSQ Patented Nov. 6, 19,45

PATET civico mimo @comme SYSTEM 4Stuart W. Seeley,

Roslyn Eeirlxio, om'ioiiii A.

Rankin, Port Weshim'lon, N Y., assignee-o io Radio Corporacion oi iimceico, o comoeoion o! Deloware Application Sepiemlcei 5, MM2, Social No., liii@ c com e.

@of loi-esem; invention Telai-,es lo milio signal ing systems, and more particularly to moduleiecl comici' signaling systems which employ o fren ouency located in che lower perfs ooclible frequency Tonge es o modulation coiiipceienl.,V

One of the mein obieci'e of our invention is izo t provide o method of iodio signaling over distances gieoiei then licei: ci. 'which emol monitoring ie i cosimo; in our syslem there is .seemed exotisme Lory sigmoiing with Teceivecl siamois me weekeithan che noise level., Toe presen@ cys'lein ilil3% effective beyond Jthe conge et which sic-clic enel loco! noises would conce coo much incerieie ence foi: enrol ononitoiiio,l l

@foe oi the impoTtoni, objects of our present low/emilion ism provide e eignolinglsysiem which lo eleciive laeiween any Teclio bioecicesisioe come@ mittel' ond only mambo? oi receiving locations; o "nel being; superimposed on 'll'ie mooiere mooieicy e ynopeziy designe@ receivezf, ce by om roem; connected to om; soaisocsow cecclcer which cuneo lo `she Another imprimant olcgleci Aof oci? .invention ie gorcoviole o iow frequency oleron "omis, f c eciociimeni; iso eienclmci meetic ce@ ceo/e1, winch sepeioies the lowii'eouency come @oT- ri me oTogiem i. e eend poso @litem ond, oitei iol lowed by amplitude limii-eiiom, ceases '-,ooeo mechanical resoooioc io eciueiecl im cee spense io tciiewiiez'eoy @Je alecm cii'coii iooilier oliiec; of our invention lolo oiovicle o foit utilizing e low iiergiaence moriuie= o component of o Received mocioleizecl com* ec weve; ille syst-em comprising en amplitude im@ licei which fee@ the looy frequency cone eleo lo degenerative inicia@ ciicuiiJ followed by lionel :meer Teeonon; lo olie loc; i'ieooency, ne llierecl cone keine culogecied lo omoiilooe prior io occoeiionoi o Teecl moed izo olie.

low frequency come, lollcolis@n time clcloy oo 3T c olie work circuit Teley cgoinst :spacious c A etico caused by stcong oresononi iones oi* .Locom longed corsie oi severe sialic oc @they inieiiew ence impulses.

oiheT oojecic oi? om invention ere loimn moge one rile-l oieiiel by memo of eels-2cm @ion itself, however, es to icoizii its organization onli method of operation Tirill best loe understood by eeference to the following* description 'teken in connection Wi'h the which We lieve indicated diogi'emmeciceliy e circuit organize lion wheieloy our invention may he corrieri into eilec'o'.

Refeiiinc, noo', 'cioe accompanying chewing there ore shown the cil'cuii: det-oils of 'the elem which le e-riepi'fecl for connection to o sion@ ecol lol'ooclcect ceceivei open-,line in the 550 to i706 iiocycie (lic.) omioliisude .modulation broerlcesi, bood. En to wom oil bioedcesters in e eivemmee oi impending emeTgency, such es on eccoci; one'irensmiter of che mee is clesL1 ignote@ es iaifie key station. 'Tmc sie/cion, oi;

, ocooei signal from olie mili'eiy oT police euchoie ties, Ioyooclcesio e, Wyoming to stations isc olie Hence, einer stations e employ e, Special oi'oecces'a recelo 1 moioc elle key ciclico modulation chi'oughoui; opeoiion. Socle ooiel monilzocing" ci .stem

i'eqi Tee o special moo soi iiecimcicm lo cone e lcegf etoion programs; ie

well disturb oiziiere i omelie il receives is not liep?, ogzeciel i To moei', seiioos imiiaoton oi emol is inkel' l, is limited in steile, loool noise and @11T of opemiee with eieciivemeso beyond the renee which mcoiioi'lrcgf coe im om pi'eseci; system r lice co e ploy special accendono lo momies key st only equipment comme@ to out cui cys m lolo operacion in coniuociion wiiiii ieguier loroe= ceci; @committee le consloiit=frequency, low ouency coole generator. Foi' exemple, We vFoei/e soiisfecoiy used e @il cycle lione. cone is sooeimgsoeecl on olie oioeiom mofiulesion ci the icc?? key emilion, and cle'eciecl by the i0 cycle elem?.

anni einem@ folie chewing. The ei cycle 'ione once lo che listening public. 1t must loe noted,

however, that continuous modulation at thai level will substantially reduce the power of the .trensmitter en ier as ite program handling capability is concerned. in che present; disclosure let it be assumed that the low frequency tone is applied to the carrier onlywhen it is desired to signal to the. other broadcasters inthe area that a radio blackout is to be enforced. Of course, the invention is not limited to this use. nor to the standard broadcast band. The invention may be applied to any desired frequency range so far as the carrier is concerned, and may be used for signaling information to receivers located 'in any desired place.

Numeral i denotes the diode demodulator, or second detector, of a superheterodyne receiver. The usual intermediate frequency (I. F.) transformer 2 feeds the I. F. energy, whose frequency value may be at 465 kc., to the diode detector. Load resistors 3 and are bypassed for I. F. currents by condenser 5. The condenser 6 bypasses the resistor 4. The receiver feeding the detector diode ishould be one whose sensitivity, selectivity, stability and freedom from frequency drift are suiiicient so that complete dependence can be placed on the operation of the device when the necessary low percentage, low frequency modulating tone is mixed with the program material volume control device. The plate of tube l is connected to the +B terminal of` the power supply network (not shown) through resistor 9'. The screen grid vof tube is connected to any desired point on resistor i@ by slidable tap ii; the resistor i is connected from the lower'end of resistor 9' to the grounded cathode of tube i. Bypass condenser 4i2 is connected from tap ii to ground. The noise limiter tube functions to limit the noise output by plate current cut-ofi of tube The level at which limiting starts may be adjusted by the limiter control tap ii.

The noise-limiter tube 'l functions to clip the noise peaks. Subsequent to limiting action, the

modulation energy is transmitted to the grid i3 of the degenerative input amplifier tube lli. The condenser 20 shunts resistor 9' to ground.` The condenser is connected from the limiter plate to ground in order to limit the frequency response of the limiter output circuit. iThe components, of audio frequency that are of particular interes are low frequencies lying between 20 to 40 cycles;

in this particular case icycles. Hence, the condenser 28 is employed partially to remove the higher audio frequencies. The normal audio channel of the broadcast receiver is connected to thejunction of resistors d and l. In this vway the entire range of audio frequencies will be transmitted through the condenser 3 to the usual audio volume control potentiometer il. .The usual audio amplifiers and reproducer' will follow the volume control device li'. y l

The grid i3 of tube ifi is connected to ground by grid return resistor il, The grounded sheath i8 shields the input lead to grid i3. The cathode i6 is connected to a point of -90 volts through-an unbypassed resistor 2d. The plate i5 of tube i6 is connected to a point of +325 volts through series resistors 25A and 2d; the condenser 2 bydenser 3 i passing resistor 26 to ground. The degenerative input amplifier is designed to be extremely ilexible. As long as the tone signal at the input grid i3 is greater than 1A volt peak to peak, and the entire applied audio components do not exceed- 100 volts peak to peak, operation will be satisfactory. An additional reason for employing a degenerative input amplifier is to eliminate the possibility of istortion and cross-modulation.

In order to removke the program componentsv tion of 28-3! to ground. Circuit 3i), similarly tuned to 40 cycles, is connected at its high alternating potential side to the grid terminal of con- Condenser 32 connects the low potential side of circuit Si) to ground. The grid of tube 33 returns to the junction of resistors 36 and 35 through the coil of circuit 30.

The filtered cycle tone isamplified by tube 33, whose plate returns to the plate supply lead 36 through a resistive load 3i. The resistor 8l is tapped by bypass condenser 39. Condenser 4d,

of low impedance to program frequencies, by-

passes the upper end of resistor 3l to ground.

The amplified 40 cycle tone is applied to a second- 4 The second limiter prevents excessive amplitude against having the system operated by exceedingly strong off-resonant tones or prolonged bursts of severe static or other interference.

The output of limiter li is applied to the reed amplifier d8, the grid it of the latter being coupledby condenser 50 to the plate of tube ii The cathode of tube l is connected by resistor 52 to ground, while grid i9 is returned to ground by resistor 5|. In the plate circuit of tube d8 there are arranged in series the winding B of a reedactuating electromagne't and choke coil 53. The choke 53 is employed to prevent any 40 cycle cur- Yrent (the plate current of reed amplifier dil) from iiowing back through the +B supply impedance,

and causing overall regeneration. The lower end.

of winding B is bypassed to the cathode of tube d8 by condenser Sli. The upper end of choke 53 is bypassed to ground'by condenser 55. The reed .iiowing through the win'ding B is of 40 cycles.

Hence, the reed is a highly selective device. The upper end of reed 5d is provided with a contact point. 'I'his contact pointY is arranged in spaced relation to a second contact point. The spaced contact points are denoted by numeral 51. When the contact points 51 touch, a circuit is completed through them for energizing a subsequent relay. The contact point 51 secured to the reed 56 is connected through lead 56 to the control grid S of the following direct current (D. C.) ampliiier tube 60. The grid 59 is connected by the low leakage condenser 6| to the line 36.

The second contact point 51 is connected through resistor 62 to the adiustable arm 63 of a time delay circuit. The adjustable arm 63 is arranged to be selectively connecd to a condenser 64, a condenser 65 or a condenser 66. The lower end of each oi these condensers is connected to the -90 volts line 61. The upper terminal of each of the time delay condensers has a contact to which may be connected the adjustable arm 63. It is indicated on the drawing that when arm 66 connects condenser 64| in circuit, then there is a time delay of 5 seconds. The connection of 63 to condenserv 65 introduces a delay of l0 seconds,.and connection of arm 63 to condenser 66 introduces a delay of 20 seconds.

The lower end of resistor 62 is connected through resistor to the positive energizing line 36, and the grid condenser 6| has its lower terminal connected to the lower end of resistor 10. The control grid 59 of tube 60 is connected by resistor 1| to the negative biasing line 61, while the cathode of tube 60 is connected to ground. A switch 60 is arrangedin shunt relation to the grid return resistor 1|. The switch 80 is arranged for simultaneous adjustment with a second switch 8| whoseiunction it is to control the energizationv of the winding A2. One end of the Winding may be connected through switch 8| to ground, while the other end is connected to the screen grid energizing lead 82, which provides the screen grid voltagefor the screen grid of amplifier tube 60.

In other words, when switch 8| is closed the winding A2 is energized. A second winding A1 is arranged in the plate energizing circuit of tube 69. We have schematically represented windings A1 andAa as controlling the. schematicallyrepresented, circuit-closing armature 90. Here,

, again, the armature 90 and the energizing electromagnets therefor are schematically represented, since they are well known to those skilled in theart. For the purpose ci this application` it "is believed suflicient schematically to represent these elements. It is suiilcient for this application to point out that armature 90 will be drawn towards the core around which winding A; is wound. Upon the attraction of armature 60 the 115 volt outlet |00 will be in electrical connectionf with the 60 cycle alternating current source. Any electrical device may, therefore, be plugged into the outlet |00, andwill be energized. For example, an electriclamp, bell or siren device may be inserted in outlet |00. When armature 90 is drawn towards electromagnet A1, the armature contact 9| will come into electrical contact with contact point 92 which is connected by lead 93 to one side of the outlet |00.

As long as switch 8| is open, the-electromagnet A2 will not be energized from the +S source. However, when'switch 8| is closed electromagnet winding A: is energized, and it is so arranged with respect to armature 96 as to pull the armature away from that position'in which there is electrical contact between 9| and 92. Inl other words, the alarm circuit will now bebroken. Concurrently, with closing of switch 6| switch 80 is closed. This renders the amplier 60 ineffective,

and thus'causes de-energization of the electro magnet winding A1. We have, therefore, designated switches Bil-3| as Alarm. release push button.

It has been previously pointed out that the limiter 4| acts to prevent operation by exceeda ingly strongA oli-resonant tones, or prolonged bursts of severe static or other interference. Further protection against spurious operation is obtained by the time delay control circuit. This time delay circuit can be adjusted so that the work circuit relay winding A1 will be energized only after 5, 10 or 20 seconds ol' sustained tone at the correct 40 cycle frequency. Associated with the reed 56 is a pair of electrical contac 51 which are closed solely when reed vibration has built up to a suiilcient amplitude. These corrtacts 51 are connected to the time delay circuit which energizes the electrical relay windingV A1 after a predetermined time ci continuous reed vibration. It will be understood that the work circuit relay is of the latching type with sumcient contacts so that several functions may be performed. These may include the ringing of an alarm bell, switching of the loudspeaker of the receiver, and vany'other functions. The reed 56 should be tuned to the exact operating frequency. High capacity filter and bypass condensers should be used throughout the system, not only to reduce hum components but also to prevent regeneration at extremely low frequencies of 1 to 10 cycles per lsecond through common coupling in the +B supply. To explain the functioning of the time delay control circuit in iurther detail, when the device is inoperative (reed not vibrating) contacts 51 are open and the grid 59-will be biased to -90 v. relative tothe cathode which is at ground. This means that condenser 6| is charged to +325 v. --(-90 v.) or 4,15 v., with the positive charge on the +B side and the negative charge on the grid side. Condenser 64, 65 or 66, depending on the location of switch 63, (assume condenser 65 here being used) is charged to an equal voltage as condenser 6| (415 yv.). The negatively charged plate of condenser 65 is connected to the -90 v. line, while the positively charged plate is connected to resistor 62.

When the reed 55 is caused to vibrate, contacts 51 are closed thereby connecting the two condensers 6| and 65 together through resistor 62. 'Ihe latter is included only to reduce the sparking of contacts 51. Contacts 51 close each V40 oi' a second, and as explained above connect the two condensers 654 and 6|, but the polarties off the two connected plates of the condensers are opposite. Hence, from the standpoint of condenser 6| the charge across it is reduced. During the time (each cycle) that contacts 51 are open, conf denser 65 again charges up to its initial value of 415 v., due to the short time constant of con- I u denser 65 and resistor 10 (l meg. 720 mm'f.=.00012 second) Y ampliiier'60 thereby closing the relay in its plate circuit.

ADue to thev large difference in value between each of condensers 6I, 65 or 66 and condenser 6| the amount of change of charge on condenser required to reduce the charge on condenser I suiciently to permit grid 59 to reach zero bias.

The times indicated on vthe drawing adjacent each of condensers $4, 65 and 60 are approximately correct. This means, for example, that with condenser in circuit the contacts 5l are closed 10 sec.x40 cycles/sec.=400 times, before the relay 90-9i is closed.

2,888,576 .Il resulting lfrom each closing of contacts 5'! Field tests with this type of alarm unit are highly satisfactory. In one test a 50 kilowatt transmitter operating at 750 kc. (WSB) was received by equipment located 290 miles away (airline separation) aty WJAX, Jacksonville, Fla. Broadcast reception in this area is haphazard. vUsing the present system of low frequencysignaling 100% operationy was had. The receiving equipment was located near the center ofthe city where high intensity local noise is common. In another test perfect .perfomance of the system was had in an airline distance of 145 miles between transmitter and receiver. In this test the daytime static was suiilciently severe to make the signal completely unusablefrom a monitor point of view, but had no effect on the ries of eld tests, conducted in the New England area. perfect performancewas obtained on a 50 kilowatt transmitter under severe noise conditions at 355 miles. Perfect performance was ob- Cai do dn Cn.. -..micro-microfarads-.. Css f do Cu y fin 2,500 Les henries-- 42 While we have indicated and described a system for carrying our invention into effect, it will be apparent to one skilled in the art that our invention is by no means limited to the particular organization shown and described, but that many modiiications may be made Without departing from the scope of our invention, as the appended claims. What we claim is: 1. In a signaling system adapted Cas to receive carrier wave energy modulated with a low frequency,

a demodulator for providing energy of said low undesired noise impulses; a band pass filter, tuned to said low frequency, connected t0 the limiting low frequency signaling system. In another setained in the interference area between two syngiven in order to aid those sinned' m the srt to construct the present system:

Rm ohms 25,000 Re' rio- 250,000 Ri megohms-- 10 RM ohms-- 39,000 Rss yrin 47,000 Rss do 30,000 Rt dn 156,000 Rss dn 5,600 Rss rin 68,000 Re megohm-- l. Rss ohms..- 50,000 Rn rin 560,000 Rm do 578,000 Rsi megohm-.. l R32 ohms-- 820 Rca do........ 10,000 'Ran mpg0hm 1 Rn megohms-- 20 Cm ....microfarads-- 1 20 Cm micro-microfarads-- 1,000 C21 -microfarads..- 20 Cri do 0.1 C11 rin 0,1 Css M don-.. 15 @se 'dn 8 @te fin 0.05. C@ in 0.01 Cs dn 0.01 dn means, an alarm circuit, means for controlling the 4operation -of the latter, and a highly selective device, responsive directly to the lter output low frequency energy, for rendering said controlling means eiective and an adjustable time delay means connected to said selective device, said time delay means consisting of a plurality ofcondensers of different sizes providing a time delay range of 5 seconds to'20 seconds.

2. In combination with a system adapted to derive a low audible frequency control tone from a radiated modulated radio carrier, a band pass filter tuned to the control 'tone frequency, an alarm circuit, a highly selective mechanical reso-f nator, tuned to said control frequency, coupled to said filter output for direct energization by the control tone energy, means responsive to actuation of the resonator for controlling said alarm circuit, a time delay control means, consisting of a plurality of delay elements of respectively different time delays and means for selecting a desired one of the delay elements, for preventing spectively dierent magnitudes to provide correspondingly different time delays, a selective device for connecting a desired one of the con--` densers to said circuit-closing device, said reed being tuned to the signal frequency, means for vibrating said reed with solely the lter output energy, and an amplitude limiter and a degenerative amplifier arranged in cascade between said source and lter input terminals to prevent spurious operation of the reed by undesired impulses.

STUART w. SEELEY. 'i

set forth in 

